Automatic telephone system



June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONE SYSTEM Filed April 29,1955 6' Sheets-Sheet l INVENTOR. HARRY F? MAHONEY W ATTORNEY.

awn-2E June 1, 1937. H. P. MAHONEY 2,082,586

AUTOMAT I C TELEPHONE SYSTEM Filed April 29, 1935 6 Sheets-Sheet 2 as QS I N N 4. 2% N H $6 5! 2 N o x I a F w Q m 4 4 E :3 Hi. i? g m p m 1 I:V E

w m 9 Q N e: :I u N N N k9 41 Q N II 4 4 U Us *1 1 j CONNECTOR HARRY P.MAHONEY ATTORNEY. V

June 1, 1937. H. P. MAHONEY 2,082,586

AUTOMATIC TELEPHONE SYSTEM Filed April 29, 1955 6 Sheets-Sheet 3 J6] Eax 4 CONNECTOR CONT.

- HARRY P. MAHQNEY ATTORNEY.

June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONE SYSTEM 6 Sheets-Sheet 4Filed April 29, 1935 June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONESYSTEM Y m R s o m t T w b m wE W A mm W U. W M R S o I t l q UK a nun1.. W & \r 3E 5E m 6 1 H m w u H 5 Y B 1 &%2E fix? v l n v 1 m Q. TT llMWMMMMMMMW A b 1 I... H j n 1% a 4. m3 2 8m F 5534 Q S. l 98 mNm 7 HI 11 I! A $325 w .f I11 E85 I 4! 223 IL I 3.5% T I b QE AB F 5 NB 1L w\le'.

0 Q h w m m N ATTORNEY.

June I, 1937. p, MAHONEY 2,082,586

AUTOMATIC TELEPHONE SYSTEM Filed April 29, 1935 6 Sheets-Sheet 6 H J l O01 a a2e' sa1 529 sea 2 'i INVENTOR.

l HARRY P. MAHO NEY BY ATTORNEY.

Patented June I, 1937 UNITED STATES ATENT OFFICE mesne assignments, to

Associated Electric Laboratories, Inc., Chicago, 111., a corporation ofDelaware Application April 29, 1935, Serial No. 18,774

7 Claims.

The present invention relates in general to automatic telephone systems,but more especially to automatic systems of the Strowger step by steptype, and the object of the invention is to produce a better and cheapersystem for use in giving service in an exchange comprising between aboutthree-hundred and six-hundred lines.

In further explanation of the object of the invention, it may be pointedout that the standard Strowger switch has a capacity of one-hundredlines. By using finders and connectors linked together in pairs anautomatic switchboard for one-hundred lines may readily be constructed,and such is the common practice for small exchanges of this size. It hasalso been found feasible to equip the finders and connectors with twosets of wipers and thus increase their capacity to two-hundred lines,which is the largest sized exchange heretofore built, so far as isknown, us-

2 ing finder connector links of the step-by-step type. 1

In the range extending from about threehundred lines to one-thousandlines it has been the practice to insert first selectors. A commonarrangement is to use finders paired with the first selectors, andconnectors arranged in groups accessible to the selectors, constitutingwhat is commonly known as a one-thousand line system. This larger typeof system is more expensive per line than the one-hundred line ortwo-hundred line system hereinbefore referred to, because it introducesan additional order of switches.

In view of the facts stated in the foregoing, it will be understood thatthe manufacturer is somewhat handicapped in selling automatic equipmeritfor exchanges which are just a little too large for a simple finderconnector link system. A system of the one-thousand line type has to beused, which results in a sudden rise in the cost per line, whichalthough entirely justified by the equipment which has to be supplied,is nevertheless diflicult to satisfactorily explain to the customer.

More specifically it is the object of the present invention to devise asystem which will fill the existing gap between the one-hundred line ortwo-hundred line system and the one-thousand line system, by producingan exchange in this capacity range which can be sold at a cost per linecomparable with the cost per line of the smaller system and considerableless than the cost per line of the one-thousand line system.

The object is accomplished by new and improved arrangement for mountingthe switching 5 equipment and by new and improved circuits which makesit possible to use finders and connectors of much larger capacity thanhas heretofore been considered possible. In a representative system,such as will be described herein, the switching equipment comprisesfinder connector links, each finder and each connector having four setsof wipers, which gives them access to four-hundred lines. Thus a systemis produced capable of giving service in an exchange of this size, andat the same time the necessity for 'pro- 0 viding first selectors isobviated. The system is arranged so that additional banks and wipers mayreadily be added to increase the capacity to six-hundred lines wheneverthe occasion should arise. 15

Further details of the system will be explained hereinafter inconnection with-the drawings, in the course of a full explanation of theequipment and circuits of which it is comprised.

Referring to the drawings, Figs. 1 to 5, inclusive, 20 are circuitdrawings which show the circuits which are necessary to enable thesystem to be explained; while Fig. 10 shows how the circuit drawings areput together. Of these circuit drawings, Fig. 1 shows a line circuit anda finder switch, 25 Figs. 2 and 3 show a connector switch, while Figs. 4and 5 show two allotters with the associated common start wires. Figs. 6to 9, inclusive, show certain mechanical features of the system. Ofthese drawings, Fig. 6 shows a por- 30 tion of a switchboard with one ofthe link circuits mounted thereon, while Figs. 7, 8, and. 9 show certainmechanical details of the switches which cannot be shown clearly in Fig.6.

The general arrangement of the system will 35 first be describedbriefly. There are four-hundred lines. The majority of these lines aresubscribers lines, but a few of them maybe trunk lines extending toanother exchange. Each line is provided with a line circuit comprisingtwo relays. Thus 40 the line shown at the left of Fig. 1 comprisingconductors IIlI and I02, is provided with line equipment consisting ofrelays I08 and IE1. Relay IEl'I is a combined line and cut-off relay,while relay lot is a lookout relay. From the line circuit conductors areextended to the multiple banks of the finder switches. There is also abranch for each line which extends to the banks of the connectors. Thusin the case of the line shown, 50 the branch which extends to theconnector banks comprises conductors I03, I04, and I05.

All connections in the system are set up by means of finder connectorlinks, each link comprising a finder switch and a connector switch.

' level of the finder switches.

These switches are of the well known Strowger vertical and rotary type.Each finder and each connector is provided with four sets of Wipers sothat it may have access to all four hundred lines of the system. Theremay be around thirty links, more or less, depending on the amount oftraffic.

The subscribers are assigned numbers beginning with the digits 2, 3, 4,and 5, that is, the second, third, fourth, and fifth hundreds are used.Subscribers numbers all have four digits, of which the first three areline selecting digits while the fourth is a party selecting or ringingcurrent selecting digit. Trunks may have two, three, or four digitnumbers, depending on factors which will be explained.

While the link circuits are all in one large group from the standpointof each link being able to serve all the lines in the system, these linkcircuits are nevertheless divided into two groups as regards thearrangements which are provided for starting the finders. The lines aredivided into groups A and B, the lines which have nunibers in the evenhundreds constituting group A, and the lines which have numbers assignedin the odd hundreds constituting group B. The finders are divided intotwo corresponding groups, the basis of the division being that thefinders of group A normally serve the lines in group A, while thefinders in group B normally serve the lines in group B. It will beunderstood, however, that each finder has access to all the lines, asstated hereinbefore, and if no finder in group A is available at thetime that a line in that group makes a call, then a finder in group Bwill be taken for use. The same is true as regards lines in group Bcalling when no finders in the associated group are available.

The starting of finders is controlled by means of two allotters. Fig. 4shows allotter A which is associated with the finders of group A, Fig. 5shows allotter B which is associated with the finders of group B. Thefinder switch which is shown in Fig. l is a finder in group A, and'consequently is accessible from the bank of allotter A, Fig. 4, asindicated by the cable including conductors 458, etc. The allotter A maybe a 25-point switch of the type which has a movement in a forwarddirection only. Only one set of contacts is shown, being the set ofcontacts which is assigned to the particular finder switch shown inFig. 1. The other sets of contacts are individual to and are wired tothe other finders of group A. Allotter B in Fig. 5 is similar to theallotter A, Fig. 4. Allotter B is associated with the finders of group Band the various sets of contacts in its bank are wired to the finders ofthat group, the same as the contact sets of allotter A are wired to thefinders of group A.

For each group of lines there are ten common start leads. The commonstart leads for the lines of group A are shown appropriately labeled atthe left of Fig. 4. There is one start lead for each tens group oflines, corresponding to each The common start wires are accordinglynumbered for convenience from 1 to 0. Each common start lead isconnected by way of a resistance to a main start conductor M3, whichextends to the allotter A.

Each line circuit is provided with an individual start lead. The mannerin which these individ ual start leads are connected will now be eX-plained. The individualstart lead for lines I I to H] of the secondhundred. and for lines H to ID of the fourth hundred are connected tocommon start lead No. 1 of the A group, Fig. 4. The individual startleads for lines 2! to 20 of the second and fourth hundreds are connectedto common start lead No. 2, while the individual start leads for lines3! and 30 of the second and fourth hundreds are connected to the commonstart lead No. 3, and so on. Thus it will be seen that as regards theline shown, which belongs to the fourth hundred, the individual startlead H5 is connected to the No. 3 common start lead. The manner in whichthe other individual start wires of group A are connected up will beclear from the foregoing. As regards the individual start leads for thelines of group B, these are connected up to the common start leads Bshown in Fig. 5 in the same way that the connections are made in groupA.

The common start leads not only function as a means of starting thefinder switches through the medium of the allotters, but they also serveto mark the levels in the finder banks in which calling lines arelocated. Each finder switch is provided with a so-called vertical bank,the vertical bank of the finder switch, Fig. 1, being indicated at 28.it will be seen that the energization of relay 48! associated with theallotter A is effective to extend the common start leads 5 to 53,inclusive, by way of cable di t to the vertical bank contacts l to 9,respectively, of vertical bank 28. The cable 414 is common to allfinders of group A and the conductors thereof are multiplied into allthe vertical banks such as 28 which are associated with such finders.

By reference to Fig. 5 it will be observed that relay 59! has thefunction of connecting all the common start leads of group B by way ofcable 414 to the vertical banks of the finders of group A. This relay511i is energized whenever a finder in group A is started up to find acalling line in group B.

It should be pointed out also that there is a cable similar to cable lit which extends to the vertical banks of the finders in group B. Relays592 and 82, under control of allotter B, serve to connect the commonstart leads of groups B and A to this cable. The conductors leading tothe right from relay contacts of relays 492 and 502 are appropriatelylabeled to indicate the foregoing arrangement. All of this will be moreclearly understood from the detailed explanation of the operation of thesystem.

The mechanical construction of the switchboard and link circuits willnow be described, reference being made to Figs. 6 to 9, inclusive.

Referring to Fig. 6, the frame of the switchboard comprises two U-shapedchannel members 2 and 5, which form the ends of the frame, and twointermediate members 3 and "3 of angle iron. These four frame membersare secured together in the relative position shown in the drawings bymeans of a transverse channel member l l,together with a similar membernear the top of the frame. There are also corresponding channel membersdirectly opposite these members on the other side of the frame. Theupright frame members 2, 3, 4, and 5 are attached at the bottom to footmembers such as 6, 8, 9, and '1, respectively, by means of which theswitchboard is secured to the floor. The various frame members arepreferably secured together by welding. To give an idea of thedimensions of the frame it may be stated that the distance from theoutside of channel mem her 2 to the outside of channel 5 is about 63inches. The height of the frame is sufiicient By reference to Figs. 1and 4 so that fifteen links similar to the one shown in Fig. 6 may bemounted one above the other. Since all these links are the same it hasbeen considered necessary to show only the lower part of the frame withone link mounted.

On the opposite side of the frame mounting space is available for theline relays and for the necessary power and supervisory equipment suchas is customarily furnished. At the top of the frame the necessaryterminal strips are provided. These arrangements, however, are inaccordance with standard practice and need not be shown. If the traflicis light enough so that fifteen links will take care of it, then all theequipment for the exchange may be mounted on one frame. In most cases,however, as many as 25 or 30 links will have to be provided to take careof the traffic, and it follows that two frames will have to befurnished.

Considering now the link which is shown in Fig. 6, the apparatus ismounted on a base plate Ill. This base plate is a U-shaped steelstamping corresponding in length to the distance between angle irons 3and 4 and about 5 inches Wide. The plate is bent at right angles alongthe upper and lower edges shown in the drawings so that there is arearwardly extending portion about three-fourths of an inch wide alongeach edge which bears against the face of the angles 3 and 4. By meansof machine screws shown in the drawings the base plate It is secured inposition on the angle irons 3 and 4. This base plate l0 carries thefinder switch mechanism at the left, and the connector switch mechanismat the right, and the finder and connector relays, such as are shown inFigs. 1, 2, and 3 of the circuit drawings, in between.

The connector switch is of the usual vertical and rotary construction.Only the lower portion of the frame It is shown in the drawings, therest of the switch mechanism, except for the shaft and wipers, beingindicated by the rectangle l4. On the channel 5 there is secured abracket 24 and between this bracket and the frame I6 of the switchextend the usual bank rods ll, except that these rods are, of course,much longer than is usually the practice and are secured firmly at bothends instead of being attached only at the switch frame. On the bankrods are mounted six banks such as IS in the usual manner. The switchshaft is indicated at 21. The shaft has a bearing in the upper end ofthe switch frame and also a bearing on the lower end of the frame,exactly as in the usual switch. In view of the length of the shaft anadditional bearing is provided by the cross member 25, which extendsbetween the two bank rods I7 and i8. On the shaft are mounted four setsof wipers, each set including two line wipers and a test wiper, and alsothe vertical wiper 329.

In order to provide for connections to the wipers a special arrangementis provided which comprises a strip 23, which is attached to the banksas shown in Fig. 9. The clamping plate 69 of the second bank from theleft, Fig. 6, is provided with an ear 69, as is also the correspondingmember of the fifth bank from the left. The strip 23 is secured to theseears 69 as shown in Fig. 9. On the strip 23 is mounted the vertical bank328, and also the terminal blocks 2| and 22. The usual flexible wipercords are run between the wipers and these terminal blocks. This avoidsthe use of the unusually long wiper cords which would otherwise berequired.

The reference character 26 indicates the Well known rotary control bank.This comprises an arc shaped strip of metal which is drilled withone-hundred holes corresponding in position to the different positionsof the wiper 326. These holes are tapped and threaded pins are insertedin the holes which correspond to switch positions in which the rotarycontrol circuit is to be closed, as will be explained more fullyhereinafter.

Associated with the connector there is a minor switch, indicated in Fig.6 by the reference numeral I 5. This minor switch is of the usual wellknown construction and the circuit arrangement thereof is shown in Fig.3. As indicated in Fig. 6 the minor switch 15 is mounted on the baseplate i6 like the relays, and occupies the same space as two relays.

One object of mounting the links as shown, with the switches in ahorizontal position, is to enable the vertical magnet to operate theshaft. In the usual arrangement, the shaft stands in a vertical positionand the vertical magnet raises it against gravity, the shaft beingrestored by gravity upon the release of the switch. Due to the length ofthe shaft in the large capacity switch herein described, and the numberof wipers which it carries, the shaft is much heavier, than isordinarily the case and for that reason the horizontal mounting is muchpreferable. However, it can be seen that when the switch is mountedhorizontally gravity cannot be depended on to restore the shaft andother means must be provided. This means is illustrated in Figs. 7 and 8of the drawings. Referring to Fig. 7, this drawing shows the entire topor left-hand por tion of the connector, including the upper portion ofthe frame 16. The drawings incidentally show the manner in which theswitch frame is attached to the base Hi. There is also shown the upperportion of the shaft 2! with the helical spring for restoring it tonormal in a rotary direction. Also the normal post 4! and thecomb-shaped member 42 for controlling the level springs such as 354.These details of the switch are Well known, but if necessary referencemay be made to U. S. Patents Nos. 1,913,440 and 1,888,- 70.0.

The restoring means for the shaft comprises a bracket 46, seen in Figs.7 and 8, which is held in place under the adjusting nuts for thevertical magnet coils. At the right end of member 66 there are twoupwardly extending ears 4! and 48 between which is pivoted a lever #39.This lever is provided with an arm 50, and there is a spring 5!connected between the end of this arm and the forward end of bracket:36, as clearly shown in Fig. 7. The end of the lever 49 bears on themember 44 which is secured to the shaft 21. This member 44 is ofstandard construction except that it is provided with an ear as shown inFig. 8. With this arrangement it will be clear that when the shaft 2'!is operated it will tension the spring 5| by means of lever d9. When thedetent is withdrawn from the shaft upon release, spring 5! will restorethe shaft by means of lever 49.

The finder switch mechanism mounted on the left of the base plate ii] isindicated by the rectangle Bi]. The mechanical construction of thefinder is similar to that of the connector, except that no level springsare provided. The restoring means for the finder is the same as that ofthe connector. The-drawings show the finder shaft 3! and the wipers suchas I28 and the associated banks, also the vertical bank 28 and theverticaltest wiper 29.

It will be observed that in the case of both the finder and theconnector the switches are shown equipped with six banks, which issufficient for a capacity oifour-hundred lines. Provision is made,however, for adding three more banks to each switch, so as to increasethe capacity to six-hundred lines. In the case of the connector shown inFig. 6, one of these additional banks would be added tothe left of thebearing member 25 and two of the banks would be added between thishearing member and the bracket 24. Thus the design of the links is suchthat the system may be installed with an initial capacity of eitherfour, five, or six-hundred lines. The circuit shown in Figs. 1 to 5,inclusive, is arranged for a system of four-hundred lines, but canreadily be adapted to take care of either fivehundred or six-hundredlines by a simple extension of the plan of wiper selection which isillustrated.

The operation of the equipment in setting up a number of representativeconnections will now be described. The first connection which will beconsidered is a call from station 43! 2, on line |0|l02, to anothersubscriber in the system whose number will be assumed to be 33 [2.

Upon removal of the receiver at station 43R, the subscribers talkingequipment is bridged across the line, thereby closing a circuit over theline conductors iflli32 for the combined line and cut-off relay I01. Itwill be observed that the three windings of relay It! are connectedacross the line in series with the battery. The upper winding of relay I!ll is made of wire having high resistance, so that the relay isinefficient under these operating conditions and pulls up only part way,closing the contacts marked X and leaving the position of the othercontacts unaltered. The closure of the upper contact X places batterypotential through the middle winding of relay It}? on test contact H8,thus marking the line as calling in the banks of the finders such as thefinder shown in Fig. 1. The closure or" the lower contact X placesground on the individual start wire H9.

Since the individual start wire H9 is connected to the No. 3 commonstart lead, Fig. 4, a circuit is completed which extends from thegrounded common start lead by way of M0, M3, 428, and 425 to relay istof the allotter A, Fig. 4. Relay 494 accordingly energizes. At 422 relay4M closes a circuit for relay MN, and the latter relay upon operatingconnects all the common start leads by way of M4 to the vertical testbanks of the finders in group A. Thus a ground is placed on the No. 3test contacts in these vertical test banks, including the No. 3 testcontact in bank 28, Fig. 1. The energization of relay lii i also opensthe circuit of relay 495 at 52! and closes a circuit for relay 49! at420. Upon energizing, relay 401 closes a locking circuit for itself at833. In addition, relay iill closes a circuit for relay 689 at $34, anda circuit for relay M6 at 435. The latter circuit is to guard againstrelease of relay 406 in the event that only one finder switch isavailable, as will be explained more fully later on. Relay lilil alsoshifts the circuit of wiper 453 at 43%} for reasons to be presentlyexplained, prepares the test circuit at Q32 for test relay Mil, and at43l places ground on the wiper 45L This latter operation grounds theindividual start wire e56 extending to the finder shown in Fig. 1.

When the circuit of relay 409 is closed, this relay operates, at 43'!prepares a locking circuit for relay 4 l 0, at 439 closes an impulsingcircuit for the finder, Fig. l, and at 438 attempts to close a circuitfor relay 4| I. The contact engaged by spring 4-38, however, is weightedand upon the operation of relay 589 this contact is set into vibrationwith the result that the circuit to relay ii! is intermittently openedand closed. Relay iii cannot operate under these conditions. As a matterof fact, this relay never does operate if the calling line is found inthe normal manner. The function of relay ll! will be fully explainedlater on.

The effect of grounding the individual start wire 456 is to operate thestart relay I46 of the finder, Fig. 1. Upon energizing, relay H56prepares a circuit for rotary magnet M4 at I59, disconnects conductorI'M from the conductor it! at I58, shifts the circuit or the guard wire#255 at 57 in order to prepare for energizing the stepping magnet 45!;of the allotter, prepares a circuit for test relay M2 at 55, and at 56closes circuits through the polarizing windings of test relays MI andM2. These relays, however, do not operate at this time.

As already mentioned, the relay 499 of the allotter closes the impulsingcircuit for the finder when it pulls up, so that the finder is startedin its vertical movement by the time the so-called start relay 546 haspulled up. The circuit for the vertical magnet extends from ground byway of M8, 439, 336, 444, 454, and 459 to vertical magnet M5. On theclosure of this circuit the vertical magnet of the finder energizes andadvances all the sets of wipers into position opposite the first levelsin their respective banks, at the same time shifting the ofi normalsprings E68 and E65. understood that the vertical movement is in realitya horizontal movement in view of the way the switches are mounted, butit is thought that the explanation will be clearer if the familiar termvertical is retained. When the vertical magnet M5 energizes it alsogrounds conductor 468 at Mt, thereby operating the stepping relay 468 ofthe allotter. Upon energizing relay @598 opens the circuit of verticalmagnet M5 at 436, whereupon the vertical magnet fa'lls back and opensthe circuit of relay 4B8. Relay 488 then falls back and again closes thecircuit of vertical magnet H55, causing the magnet to advance the switchwipers another step. This operation in which the vertical magnet andrelay M33 are alternately energized continues until upon the third stepof the vertical magnet the vertical test wiper 29 arrives at the No. 3test contact in the vertical bank 28.

The operation of stopping the vertical move" ment will now be explained,Upon the third step relay 40!; of the allotter energizes by way of i5!and opens the vertical magnet circuit at 136. The vertical magnetaccordingly falls back and breaks the circuit of relay 398 at 15L Relay468, however, does not fall back but remains held up over a circuitwhich extends from the grounded No. 3 test contact in the vertical bank28 by way of 29, .58, 453, Mill, upper winding of the test relay M0,432, and winding of relay 308. Relay ME! energizes over the abovecircuit in series with relay 408, the latter relay holding up as statedprevents the circuit of the vertical magnet from again being closed.

Upon energizing, the test relay llll locks itself at MI and also closesa circuit for relay M2. The latter relay pulls up and attempts to closea circuit for relay il I, but without effect under normal conditionsbecause the contact engaged by spring 449 is constructed similar to thecontact It is engaged by spring 438 of relay 409, the operation of whichwas previously described. Relay II also opens the initial energizingcircuit of relay 401 at 442, but relay dill holds up over its lockingcontact 433. By opening contact A43 relay Mil prevents the energizationof relay MI by way of the circuit previously closed at contact 433 ofrelay see. At MM relay Mil shifts the impulse or operating circuit fromconductor 59 to condoctor @82, thus accomplishing the change over fromvertical to rotary operation at the finder, Fig. 1. At Mil, relay lifigrounds wiper 453 and also breaks the circuit which includes the upperwinding of relay II!) and stepping relay 408. The latter relay now fallsback in order to start the rotary movement of the finder switch, Fig. 1.

It will be understood now that all of the four sets of wipers with whichthe finder, Fig. l, is provided are standing opposite the third levelsin their respective banks. Only two of these sets are connected up,however, because relay I III has not been energized. The wiper setswhich are connected up are the set which comprises test wiper I20 andline wipers I22 and I23, this set having access to lines in the secondhundred, and the set comprising test wiper I26 and line wipers I28 andI29, this latter wiper set having access to lines in the fourth hundred.The calling line. being a line in the fourth hundred, is accessible onlyto the latter set of wipers.

As mentioned hereinbefore, the rotary movement is started by the fallingback of stepping relay 4B3, consequent upon the energization of testrelay tit. The circuit for the rotary magnet extends from ground by wayof M8, 439, 436, 464i, 462, I59, I53, and I58 to the rotary magnet I il.The rotary magnet controls the circuit of stepping relay I88 at I59 andconsequently the stepping operation during the rotary movement issimilar to that which takes place during the vertical movement. As thewipers are rotated step by step responsive to the operation of rotarymagnet Hi l, the test wiper I20 searches for battery potential on thetest contacts in the third level of its bank,'and the test wiper I26likewise tests for battery potential on the test contacts of the thirdlevel of its bank. Test wiper I20 finds no battery potential, but assoon as test Wiper I25 engages test contact MB of the calling linebattery potential is found and a circuit is closed for energizing testrelay I il. Relay I l! operates over a circuit extending from ground atthe allotter, Fig. 4, by way of M6, Q53, e53, upper winding of relay Eli, wiper I28, H3, H3, and the middle winding of cut-off relay ID? tobattery,

this circuit serving also to fully energize relay I07.

By the energization of relay I'll, the circuit of release magnet M3 isopened at I49, the rotary magnet circuit if opened at hill, the relaylocks itself at Hi1, and at its two upper contacts the callingsubscribers line is connected through to trunk conductors I79 and Ill.

The connecting through of the calling line to trunk conductors I1!) andI'll results in the energization of line relay 204 of the connector,Fig. 2. Upon energizing, relay 2M closes a circuit for the slow actingrelay 236 at 236. Relay 2% accordingiy energizes and at 238 placesground on holding conductor I12. This operation completes a holdingcircuit for relays MI and Iil'i.

When relay Iiil pulls up in series with relay IM of the finder itdisconnects ground from the start lead H9 at Md, and also disconnectsits upper and lower windings from the subscribers line at III and H2. Inaddition, relay it: connects lockout relay I06 to the holding circuit atH3. It will be observed also that at this time the holding circuit forrelay It? provides a ground potential for the test conductor I85extending to the connector banks, where the calling line is made busy.

When ground is disconnected from individual start wire I I9, relay tiltof the allotter falls back, provided there is no other line in group Awhich is in calling condition. When relay 4% falls back it breaks thecircuit of relay till which falls back also.

Returning now to the energization of test relay l ll of the finder, whenthis relay pulls up it closes at HIS a circuit which extends from thegrounded impulse or operating conductor 452 by way of 59, I53, I48, I51key K, 455, 555, and $39 to the stepping magnet 65 of the allotter A,Fig. 4. Stepping magnet 4G5 accordingly energizes and opens itsinterrupter contact, thus breaking the circuit of relay 401. Relay 40?therefore falls back and at 35 it removes ground from relay its, but thelatter relay holds up over conductor itl. In addition relay iIll breaksthe circuit of relay 489 at 434, opens its own locking circuit at $33,breaks the circuit of start relay I46 of the finder at 43I, and at 338alters the circuit which was formerly traced over wiper 459 to thestepping magnet 465 so that this circuit includes the interruptercontact of the magnet. This interrupter contact being now open, formagnet 465 is energized, the foregoing shifting of the magnet circuitresults in the opening of the circuit and the deenergizing of themagnet. When magnet 465 deenergizes, the wipers of the allotter areadvanced one step into association with a set of contacts which isindividual to the next finder. The allotter now proceeds to hunt for anidle finder under control of wiper $50. If the next finder is busy,there will be ground on the conductor corresponding to 355 and thestepping magnet 465 will reoperate to advance the wipers of the allotterinto association with the next finder, this operation continuing untilan idle finder is reached. It will be noted that relay 40! cannot pullup responsive to a new call as long as the-allotter is hunting for anidle finder, because the relay 4&1 will be short circuited by ground oncontacts engaged by wiper 459.

When the circuit of relay 4539 is broken by the deenergization of relaylfll, the said relay 499 will fall back and break the circuits of relays4H) and H2. These relays accordingly fall back also.

In the finder switch, Fig. 1, when ground is removed from conductor 655by the falling back of relay lil'I in the allotter, relay Hi6 fallsback. At I53 relay M6 prepares a circuit for release magnet I43. and atI5? ground from the off normal springs of the finder is extended toguard wire e55, thereby maintaining the finder in busy condition withrespect to the allotter in Fig. 4.

The equipment is now ready for the calling subscriber at station Q3I2 todial the number of the called station, but before proceeding with thisoperation, the explanation of the allotter and finder circuits will be.completed.

Referring to the allotter A, Fig. 4, it will be seen that relay 406 isnormally energized over common conductor 45!. This conductor is commonto all of the link circuits and has a branch at each link circuit whichis normally grounded. Thus in the case of the link shown in thedrawings, the branch of conductor Mil for that link circuit may betrasedby way of off normal spring E50, key K, and spring I58 of relay M5, toconductor i1 2. Conductor I14 in turn may be traced by way of N2, Fig.2, 249, 2M, and 291 to ground. Due to the fact that the connectionbetween conductors I14 and Mil includes the serially related contacts ofrelay I46 and the on normal contact 169 (also contacts of busy key K),it will be appreciated that whenever the link circuit is in use theconnection between these conductors will be broken and the conductor Milwill no longer be grounded at the link circuit shown. If there are otheridle link circuits in group A, however, conductor 46! will still remaingrounded.

It will be assumed now that all of the links except one are busy, andthat the remaining idle link circuit is the one shown in the drawings.The allotter A will have its wipers associated with this link circuit,due to the fact that the guard wires such as 455 of all the other linkcircuits will be grounded. If a call comes in now from one of the linesin group A, relay 406 will operate over conductor 413 as previouslyexplained, followed by the energization of relay 401. The finder, Fig.l, is operated to connect with the calling line in the manner described,

. and at the beginning of the operation the last stead of dill.

ground is removed from conductor 46! by the energization of start relayM6. Relay 406 in the allotter does not fall back, however, because it isheld up temporarily at contact 435 of relay 301. As soon as the findercompletes its operation, ground is placed on guard wire 555 aspreviously explained, and the stepping magnet 455 is energized to breakthe circuit of relay 491. This relay then falls back as in the casepreviously described, but now it breaks the circuit of relay @136, sinceconductor 4M is no longer grounded. Relay 406 thereupon falls back andat 421 breaks the automatic hunting circuit of the allotter steppingmagnet 465. Since all the link circuits are now busy all of the guardwires 455 will be grounded and unless the circuit of 665 were opened theallotter would continue to hunt indefinitely. In addition to theforegoing relay 4B6 transfers the starting circuits, as will now beexplained.

Assuming now that another line in group A makes a call, a circuit willbe completed over the main start conductor M3 by way of 4238 (relay iilldeenergized) 513, 529, 525, and relay 505 of the allotter B, Fig. 5.Relay accordingly pulls up and controls the allotter B through themedium of relay 591 to start up an idle finder in group B. The findersin group B are just like the group A finder which is shown in Fig. 1,and the allotter B is like the allotter A, so that the ensuing operationneed not further be described. It should be noted, however, that relay505 of allotter B closes a circuit for relay 402 in- By the energizationof relay 402 the common start leads of group A lines are connected tothe vertical banks of the group B finders. This is obviously essentialbecause the calling line is starting a finder of group B rather than afinder of group A.

The handling of a call from a line in group B will now be explainedbriefly. When the receiver is removed from a line in group B, groundisplaced on one of the common start leads B shown at the left of Fig. 5thereby closing a circuit over the associated resistance and main startwire 513, to relay 594 of the allotter B.

Relay 504 controls the allotter B through the medium of relay 581 inorder to start up an idle finder switch of group B. It will be observedthat relay 5% also closes a circuit for relay 562, by means of which thecommon start leads of group B are connected up in the vertical banks ofthe group B finders.

Assuming now that all of the finders of group B become busy, ground willbe removed from the common conductor 56L which corresponds to conductor585 of Fig. 4, and as the last finder completes its operation, relay 561of the allotter will fall back and permit the release of relay 5%. Uponrelay 5% deenergizing, the main start wire M3 is transferred by way of528, 51!, 429, and 42! to relay 405 of allotter A. Accordingly, anothercall coming in from a line in group B will cause the energization ofrelay 405 of allotter A, which will start up a finder switch in group A.Relay 05 closes a circuit for relay 551, which connects the common startleads of group B into the vertical banks of the finders of group A.

Attention is directed to the fact that whenever a line in group B makesa call, the finder which is started up to connect with the calling linemust undergo a wiper switching operation, since the finder wipers whichare normally connected are those which serve the lines of group A. Thiswiper switching operation is performed by a relay such as relay 145,Fig. 1. Assume, for instance, that a calling line of group B starts up afinder in group A by means of relay 405 of the allotter, Fig. 4. Whenrelay Q95 energizes it grounds wiper 452 at 423, thereby closing acircuit over conductor 51 of the finder in use to relay I40 of suchfinder. In a similar manner when a line in group B makes a call andstarts a finder in group B by means of relay 5534 of the allotter B.relay 5% will connect ground at its contact 523 to the conductor 551 ofthe finder in use, and will energize the relay of such finder whichcorresponds to relay 15G of the finder shown in Fig. 1.

In case all of the links of both groups A and B are in use, a circuit iscompleted for placing a busy tone on all the subscribers lines so thatany subscriber upon removing the receiver will hear the busy signal.When all the links are in use relays M36 and 5% will both bedeenergized. If another call comes in now from group A a circuit will becompleted over conductor M3 by Way of 622, 513, 529, and 512, to relay403. This relay accordingly energizes and applies a busy tone to all thesubscribers lines which are not engaged in conversation. Of course, anyline which is actually involved in a connection will have its relay suchas 101 energized so that the associated line will be clear. A similarcircuit to the foregoing may be graced by way of the main start wire 513to relay 403 and is eifective in a similar manner if a call should bemade from a line in group B.

It will be recalled now that when the operation of the allotter A wasbeing described it was explained that relay 4! i tried to operate at theinitiation of the vertical movement of the finder and also at theinitiation of the rotary movement, but was prevented from so doingbecause of the special construction of the contacts engaged by springs43B and M9, which introduce a delay in the response of relay 4H. In theordinary operation of the system relay ill never operates because itsfirst circuit is opened at MS upon the completion of the verticalmovement of the finder, and its second circuit is opened at 449 by thefalling back of relay M2 upon the completion of the rotary movement ofthe finder. In the event that something should go wrong, however, whichwill prevent the starting of a finder, or the completion of its verticalor rotary movement, relay til will energize. When relay 4H operates itdisconnects at 541 the common ground conductor dfil from relay 5B5,opens the impulsing circuit at M3, at 4% locks the relay 4% to thebranch conductor 5% of the common ground conductor 555i associated withthe allotter B, and at 445 also closes an alarm circuit to call theattention of the attendant to the fact that trouble has occurred. Alsoat 555 relay ill closes a circuit for stepping magnet $85, whichenergizes and breaks the circuit of relay 4M. Relay 451 falls back andalters the stepping circuit of magnet 465 to include its interruptercontact, so that the magnet deenergizes and advances the allotter onestep. Relay till falling back also opens the circuit of relay 556. After451 falls back relay M19 remains held up by 515 and 55!, as stated. Inthis manner the allotter A is held out of service, and at the same timeby the deenergization of relay 5% the main start wire 5 l 3 istransferred to allotter B, so that calls from group A may be handled byfinders of group B. If the group B finders should all become busy, thenground is removed from conductors 55! and 515 with the result thatrelays M?! and 5| l are deenergized and subsequent calls will try to getthrough by way of allotter A. In the meantime the trouble will no doubthave been fixed. At any rate, the next call will get a different finderdue to the fact that the allotter has been advanced.

The key K, Fig. 1, is a link busy key provided for the purpose ofrendering the associated link circuit busy. When this key is operated itdisconnects conductor l'M from the common ground conductor lfil, and atthe same time it connects conductor H 5 to the guard wire 455 so as tomake the associated link circuit test busy in the bank of the allotter.

Key K2, Fig. 4, is a busy key for the allotter A. When this key isoperated it opens the branch 515 of conductor 5 so as to drop back relayand if energized, and it disconnects the common ground conductor 45!from relay 455 so as to release this relay and transfer the main startwire ll-i to allotter B. The allotter B, Fig. 5, is provided with asimilar busy key K3.

Returning now to the point where the calling line was extended by meansof the finder, Fig. 1, to the connector, Figs; 2 and 3, it was describedhow the line relay 2% was energized, followed by the energization ofrelay 256 for the purpose of placing ground on the holding conductorI12. An additional result of the energization of relay 255 is theenergization of relay 258, the circuit extending from the groundedconductor H2 by way of 259 to relay 2%. Upon energizing, relay locksitself at 248, and at 246 completes a circuit which extends through thevertical off normal contacts 0N4 to relay 2l3. Upon energizing, relay2&3 locks itself at 219, prepares a circuit 1 for relay 255 at 282, andat 233 closes a circuit for relay 262. Upon energizing, relay 2l2prepares a circuit for the vertical magnet 2M at 218, and at 2'55connects dial tone to the calling subscribers line. The latter operationgives the caliing party an audible signal which notifies him that he canbegin to dial the desired station.

It will be assumed, however, that for some reason or other the callingsubscriber fails to dial, and the operations which take place under thiscondition will be described. Fig. 2 of the drawings shows two cams 284and 285. These cams are mounted on a constantly rotating shaft, and makeabout one revolution per minute. These cams and the associated contactsprings are common to all the link circuits. When relay 2 l 3 of theconnector pulls up responsive to the seizure of the link, it prepares acircuit for relay 205 at contact 282 as explained above, and if thesubscriber fails to dial, cam 284 will presently close a circuit forrelay 2&5, the circuit extending from ground by way of 0N5, contactscontrolled by 231, 282, and upper winding of relay 255. Upon energizing,relay 205 locks itself at 237, and at 235 substitutes the ground whichis associated with the springs of cam 285 for the ground which wasformerly connected to the holding conductor I12 by relay 295. About oneminute later, cam 285 Will operate its associated contact springs,thereby inserting a booster battery in the holding circuit includingconductor H2. This operation raises the potential sufiicient to operaterelay H26 in the subscribers line circuit. Upon energizing, relay Hi5locks itself across the line at cont-acts I58 and HE disconnects theline conductor it. from the finder bank at I08, and disconnects the testconductor H15 from relay H3! at I59, at the same time placing ground onthis test conductor to maintain the line busy. The opening of the lineconductor lill causes the line relay 25 in the connector to fall back,followed by the deenergization of relays 206, 268, M3, M2, and 2%. Relay265 on falling back removes ground from the holding conductor [12, whichpermits relay MI of the finder and relay l0! of the subscribers linecircuit to fall back also. Relay l ll. upon deenergizing closes acircuit at I i-5 for the release magnet I43 of the finder. The operationof the release magnet restores the switch shaft to normal, and thecircuit of the magnet is broken at off normal springs I when the shaftis completely restored.

It will be appreciated that the purpose of the arrangement described inthe foregoing is to prevent the link from being tied up when it is notactually being used in setting up a connection. The apparatus functionsas described not only if a calling subscriber should delay dialling butalso if the receiver should be accidentally displaced from the hook, orif the line should be short circuited at any point. Any of theseoccurrences will cause the link circuit to be taken for use the same ason a regular call, but if no dialling occurs the link is very shortlyfreed and the line is locked out by means of the associated relay H t.It will be noted that the locked out condition depends on themaintaining of a bridge across the line, so that whenever the troublebecomes cleared the lock out relay will automatically be released andthe line circuit will be restored to normal condition. 7

Attention is directed also to the fact that the lower winding of relay235, Fig. 2, is connected to a conductor coming from the power panelwhere it is connected to the individual fuse alarm terminal for thisparticular link circuit. If the fuse which is individual to the linkcircuit should become broken or blown out battery will be placed on thisconductor, resulting in the energization of relay 255 over its lowerwinding. If the link circuit is in use at the time, the connection orpartial connection will be released as described in the foregoing andthe calling line will be locked out, requiring the subscriber to replacehis receiver before he can call again. In any event,

the link is made busy at 236, where ground is applied to the guard wire455.

Returning again to the point where the calling line was extended to theconnector, Figs. 2 and 3,. it will be assumed that dialling begins. Thenumber of the called station, it will be remembered, is Still, andtherefore the first digit to be dialled is the digit 3. It will beassumed, however, that by some mischance the calling subscriber dials-13 digit i instead of the digit 3. This may happen by reason of faultymanipulation of the dial. A single impulse or interruption correspondingto the digit 8 may also be produced by an accidental momentarydepression of the switchhook.

When the single interruption corresponding to the digit l occurs, theline relay 2% of the connector, falls back momentarily. Relay 206 isslow to release and remains operated during the momentar 1 interruptionof its circuit. When relay 23 falls back it transmits an impulse over acircuit which extends from ground by way of 233, 2 3i, 2E3, 233, and 218to the vertical magnet 2 M. Responsive to this impulse, the verticalmagnet 25d operates and advances the shaft of the connector one step.When the shaft moves off normal, the various oif normal springs areshifted, including ON i, but relay 2H3 remains locked up by way of 2 53,259, and 2'53. The movement of the switch shaft also brings the verticalwiper 323, Fig. 3, into engagement with the first contact in thevertical bank 323. Relay 332 is energized in parallel with the verticalmagnet. Shortly after the vertical magnet has op erated, relay 332 fallsback and closes a circuit for the connector release magnet 255, thecircuit extending from ground by way of 236, 3I3, 258, wiper 323 andcontact engaged thereby, and 0N2 (now shifted), to the release magnet2E5. Responsive to the closure of the above circuit the release magnetenergizes and restores the switch shaft to normal. It will be noted thatwhen the release magnet 2 l 5 energizes it breaks its own operatingcircuit at 299. These springs do not-open, however, until the armatureis nearly operated and do not prevent the effective operation of therelease magnet, because only a momentary energization of the magnet isrequired to disengage the usual double-dog of the switch and lock itunder the release link. This construction is well known and need not befurther explained.

It will be seen from the foregoing that if the first digit dialled isthe digit l, the only result is to operate and then immediately releasethe switch, thus absorbing or cancelling the digit.

It will be assumed now that the dialling of the called number proceedsin the proper manner, the first digit dialled being the digit 3. Whenthe digit 3 dialled three momentary interruptions are produced in thecircuit of the line relay 26d, and this relay accordingly falls backmomentarily three times, transmitting three impulses over the previouslytraced circuit to vertical magnet 2M and relay 332 in parallel. Verticalmagnet 2M operates three times and advances the switch shaft threesteps. The vertical wiper 323 is thus positioned on the third contact inthe vertical bank Relay 332 is slow acting and holds up during theseries of impulses.

When the series of impulses is finished, ,relay 382 very shortlydeenergizes and completes a circuit for wiper selecting relay 303. Thiscircuit extends from ground by way of 246, 3l3, 258, 298, and wiper 329and contact engaged thereby, to

relay 303. Upon energizing, relay 303 locks itself at 324, and at 348closes a circuit for the release magnet H5. The release magnet circuitextends from ground by way of 246, 313, 258, 348, and ON 2 to therelease magnet 2l5. Responsive to the closure of the foregoing circuit,release magnet 2l5 operates and disconnects wiper 329 at 299. Also at299 the release magnet closes a circuit for on" normal relay 2| 0 whichextends from ground by way of 233, 3l3, 258, 299, 345 (relay 333 beingnow energized), upper winding of relay 213, and winding of releasemagnet 2l5 to battery. Relay 2H) cannot operate over the above circuitjust at this time because the winding of the relay is short circuited byground on the operating circuit which was formerly traced to the releasemagnet by way of ON 2. However, an instant later the switch shaft willbe restored due to the operation of the release magnet and the on.normal springs 0N2 will be shifted back to normal position, opening theoperating circuit for the release magnet 2l5. This removes the shortcircuit from the upper winding of relay 2"] and this relay accordinglyoperates over the circuit traced. Upon energizing, relay 210 looksitself at 23!, and at 258 breaks the circuit which includes its upperwinding and the release magnet 2l5, thus permitting the release magnetto deenergize. The energization of relay Zlfi opens the dial tonecircuit at 257, and also alters some other circuits which will beexplained later.

It will be seen as a result of dialling the first digit 3 of the callednumber the connector switch is operated to the third level andimmediately released again. Moreover, the operation of the switchresults in the energization of the wiper selecting relay 303, whichremains locked up after the switch releases. The energization of relay333 selects and connects up the set of wipers which comprises test wiper33I and the two line wipers 334i and 335. This set of wipers has accessto lines in the third hundred, one of which is the line of the calledsubscriber.

The calling subscriber may now dial the next digit of the called number,which is also the digit 3. Accordingly the line relay 204 falls backmomentarily three times, and at 23 2 again delivers three impulses tothe vertical magnet 2M and to the slow acting relay 382 in parallel. Thevertical magnet 2| c advances the switch shaft three steps as before.Relay 332 energizes in parallel with the vertical magnet and holds upduring the series of impulses. At the first step of the switch shaft theoff normal springs are shifted, and the shifting of DNA opens theinitial energizing circuit of relay 2| 3. The previously describedlocking circuit for relay 2! 3 is now open at 259, due to relay 2H)having energized, but relay 2I3 holds up for the time being over anotherlocking circuit which extends from ground by way of 246, 3l3, and 279 torelay 2l3. At the end of the series of impulses the slow acting relay332 falls back in due time. The deenergization of this relay does notnow ground the vertical Wiper 323 nor close the circuit of the releasemagnet H5, because contact 258 of relay 219 is now open. However, thefalling back of relay 392 does break the circuit of relay 2l3,permitting this relay to deenergize. Upon deenergizing, relay 213 breaksthe circuit of relay 2! 2, which falls back also. The only result of thedeenergization of relays M3 and M2, which needs to be noted at thistime, is the transfer of the impulsing circuit at 238 of relay 212 fromthe vertical magnet 214 to the rotary magnet 343.

The calling subscriber may now dial the next digit of the called number,which is the digit 1. The line relay 204 therefore falls backs oncemomentarily and transmits an impulse to the rotary magnet 343 inparallel with the slow acting relay 302. The rotary magnet responds tothis impulse and rotates the switch shaft and wipers one step, so thatthe various sets of wipers are brought into engagement with the firstcon tacts of the third levels of their respective banks. Relay 302operates in parallel with the rotary magnet 343. Relay 2E2 being nowdeenergized, when relay 302 operates it closes a circuit for the slowacting relay 305, said circuit extending from ground by way of 246, M3,205, and 211 to relay 305. Upon energizing, relay 305 closes a circuitfor relay 306 which extends from ground by way of 246, 280, 261, windingof relay 306, and 310 to relay 305. Relay 300 cannot energize over thiscircuit because it is short circuited for the time being by thepreviously described circuit to ground for energizing relay 305.

Shortly after the operation of the rotary magnet is completed, relay 302will fall back and break the circuit of relay 305. This operation alsoremoves the short circuit from relay 300 and the latter relay energizesin series with relay 305; Upon energizing, relay 300 locks itself at 322and also breaks the circuit of relay 305, which accordingly deenergizes.In addition to the foregoing, at 323 relay 300 transfers the impulsingcircuit from the rotary magnet 343 of the connector to the steppingmagnet 321 of the minor switch.

Summing up the operations which have taken place so far, as a result ofthe dialling of the first three digits, 3, 3, and l, a particular set ofwipers in the connector has been selected and these wipers have beenoperated first by the vertical magnet 2M and then by the rotary magnet343 and thereby brought into engagement with the terminals of the calledline. The wiper set selected is the set comprising wipers 33 I, 334, and335. By the operations referred to, this wiper set is now in engagementwith the terminal set to which test conductor 353 and line conductors354 and 355 of the called line are connected. Although the called linehas been selected the line is not tested at this time, as the testingoperation is deferred until after the operation of the minor switch hasbeen completed.

The calling subscriber now dials the last digit of the called number,which is the digit 2. Accordingly, the line relay 204 will fall backtwice momentarily and will transmit two impulses to stepping magnet 321of the minor switch in parallel with the slow acting relay 302.Responsive to these impulses, stepping magnet 321 will advance thewipers 350, 35L and 352 of the minor switch two steps, so that eachwiper engages the second contact in its associated bank. Relay 302operates in parallel with the stepping magnet 321 and upon energizingcloses a circuit for relay 305. Relay 305 accordingly energizes also. Atthe end of the series of impulses which operates the stepping magnet321, slow acting relay 302 falls back and thereby connects test relay209 to the test wiper 33 l. The test circuit may be traced from the testcontact to which test conductor 353 of the called line is connected, byway of test wiper 531, contacts of relay 304 and 303, wiper 352 of theminor switch, 3M, 318, (relay 305 being still energized), winding oftest relay 209, to battery. Relay 209 accordingly tests the called linefor the presence or absence of ground potential on its associated testcontacts.

Assuming that the called line is busy, there will be a ground potentialon the test contact with which wiper 553i is in engagement and testrelay 209 will energize. Shortly after this occurs, the slow actingrelay 305 will fall back, as its circuit was broken by thedeenergization of relay 302. When relay 303 deenergizes, a lockingcircuit is completed for the test relay 209 which extends from ground byway of 232, 253, and contacts controlled by 3E8, to relay 209. Inenergized position, relay 209 opens the impulsingcircuit at 253 andcloses the busy signalling circuit at 250. The latter operation givesthe calling subscriber an audible busy signal to notify him that thecalled line is busy.

On finding the called line busy, the calling subscriber will hang up hisreceiver. This results in the deenergization of line relay 204, followedby the deenergization of relays 200 and 208. The latter relay opensholding circuits for the various other relays in the connector that havebeen energized and relay 206 takes ground off the holding conductor I12.As a result of the ungrounding of conductor I12 relays l4! and I01 aredeenergized. The switches are released by their respective releasemagnets in the well understood manner. The circuit of the release magnetof the connector may be traced from ground by way of 291, 244, 249, andN2 to the connector release magnet 215. In parallel with the releasemagnet 2 i is the release magnet 344 of the minor switch, the circuit ofwhich extends from ground by way of 291, 244, 249, and the minor switchoff normal springs MSON to release magnet 244. As soon as the connectoris restored by the operation of release magnet 2l5, the off normalsprings 0N2 are shifted to normal position and the circuit from groundat 291 is transferred to conductor I14 of the finder switch to operatethe release magnet I43. i '1 Thus all of the equipment in the linkcircuit is restored to normal.

Returning now to the point where the busy test relay 209 was connectedup by the deenergization of slow acting relay 302, at the end of theimpulses which operated the minor switch, it will be assumed that thecalled line is idle. Under these circumstances there will be no groundon the test contact engaged by test wiper 33I and test relay 209 willnot pull up. Shortly after relay 302 falls back the slow acting relay305 will fall back, and now since the test relay 209 is not energized acircuit will be completed for the switching relay 2! I. This circuitextends from ground by way of 202, 256, 255,1ower winding of relay 21 I,318,3l4, 352, contacts of relays 303 and 304, relay 303 being energized,test wiper 33l and contact engaged thereby, test conductor 353 and thewinding of the cut-off relay of the called line to battery. The linecircuit of the called line is not shown in the drawings but is similarto the line circuit which is shown in Fig. 1. On the closure of theabove circuit the switching relay 2 of the connector and the cut-offrelay of the called line operate in series, the operation of the latterrelay serving to clear the called line in the usual manner.

When relay 2 energizes it looks itself at 212. Relay 2 also cuts in theupper winding of line relay 204 at 233, and at 26'! opens the circuit ofrelay 300. Since the minor switch has been advanced only two steps,relay 306 has no circuit through wiper 35l, and therefore itdeenergizes. Relay 21 I also closes points in the talking circuit at 204and 265, and at 210 closes a circuit for the pick-uprelay 30! in orderto start the ringing operation. The latter circuit extends from groundby way of 298, 210, contacts controlled by 3| 2, 28!, and interruptercontacts of rotary magnet 343, to relay 30!. Relay 30! energizes andlocks itself at 3l2.

The results of the energization of relay 305 are the closure of theringing circuit at 301 and 300, and the closing of a circuit at 309 fortransmitting ring back tone to the calling subscriber. The ringingcircuit may be traced from ground by way of generator GEN, interrupterI, ringing conductor labeled FREQZ, wiper 350 of the minor switch, 32I,308, 215, 235, 22L and contacts of relays 303 and 304 to line wiper 335.From this point the circuit extends out over conductor 355 of the calledline and to ground or to the other side of the line, depending on howthe ringer at the called station is connected. If the ringer is bridgedacross the line, the return path of the ringer current will be by way ofthe other line conductor 354, line wiper 334, contacts of relays 304 and303, 220, 264, 274, 307, 320, and lower winding of ring cut-on" relay2l3 to battery and ground.

When the called subscriber removes his receiver, relay 2|3 pulls up inthe usual manner and locks itself at 219. Relay 2 is now energized sothat this locking circuit can be established by way of ground, 246, 266,and 219. At 28I relay 2|3 breaks the circuit of relay 3M, and the latterrelay falls back. Relay 213 also closes a circuit for relay H2 at 283.Upon energizing, relay 2I2 completes the talking circuit at 214 and 215.The talking circuit is shown in heavy lines and need not be traced indetail. Upon the closure of the talking circuit the back bridge relay203 will pull up over the called line. Upon energizing relay 203reverses the direction of current flow in the calling line at 23| and232. This is a standard operation which is introduced in order to givesupervision to an operator if the calling line is a trunk from anoperators position. In the connection under discussion the. reversal ofcurrent has no particular function. The required connection having beenestablished, the calling and called subscribers may converse as desired.When the conversation is finished, the subscribers will replace theirreceivers. The release of the connection is controlled by the hanging upof the receiver at the calling station, which causes line relay 204 tofall back. This breaks the circuit of relay 200 which fallsback-and-breaksthe circuit of relay 203. The connection is accordinglyreleased in the manner previously described.

In the foregoing explanation it was not specified if the called line wasan individual line or a party line. The fact is that it could be either,as the. operation is the same. This means that individual and partylines may be arranged indiscriminately, and have similar four digitnumbers assigned. In case of an individualline the last digit, ofcourse, would preferably be assigned in accordance with the frequencyofringing current which is used to ring the individual lines, this beingusually the No. 2 frequency. In case of party lines the last digit ofthe number determines the ringing current or party selection. There maybe as many as ten stations on a party line. At five of the stations theringers would be connected between one side of the line and ground,while at the other five stations the ringers would be connected betweenthe other side of the line and ground. In accordance with thisarrangement, the'circuit of relay 306 is arranged so that when theswitchingrelay 2H pulls up relay 306 will dropback if wiper 35! of theminor switch is standing onany position from I to 5, inclusive. Thus theringing current frequency selected by the wiper 350 is projected outover the lower side of the subscribers line. However, if wiper 3% hasbeen positioned on any contact from 6 to 0, inclusive, relay 305 willhold up by way of said wiper 35l after the relay 2 has energized, withthe result that the ringing circuit connections to the line are reversedat 320 and 32!, so that ringing current is projected out over the otherside of the line.

The lines of the fourth and fifth hundreds are called in the same Way asthe lines in the third hundred, except, of course, that a different setof wipers is selected at the connector in use. In selecting a line inthe fourth hundred the first digit dialled is the digit 4 and it followsthat the vertical wiper 329 will be set on the fourth contact in itsbank when the first digit is dialled, resulting in the energization ofrelay 304 instead of relay 303. The operation of relay 304 connects upthe set of wipers which comprises test wiper 336 and line wipe'rs 228and 339. In calling a line in the fifth hundred, the first digit dialledwill be the digit 5. Since the Verti-- cal wiper 329 is set on the fifthcontact in its bank responsive to this digit, both relays 303 and 304will be energized. By the operation of both these relays simultaneouslythe set of wipers which comprises test wiper 331 and line wipers 340 and34! is connected up. Otherwise the operations are the same as theoperations which have already been described. The lines in the secondhundred are called by means of the normally connected set of wiperswhich comprises test wiper 330 and line Wipers 332 and 333. Since thisset of wipers is normally connected, the calling of a line in the secondhundred does not involve the operation of any relay such as 303 or 304,and consequently is somewhat difierent. This can conveniently beexplained later in the course of the description of the establishment ofa trunk connection, as the groups of trunk lines are assigned numbers inthe second hundred and are accessible to the normally connected set ofwipers.

Before taking up the establishment of trunk connections an additionalfeature of the regular exchange operation will be described. Thisfeature is the handling of revertive calls on party lines. A revertivecall is a call from one subscriber on a party line to another subscriberon the same line, and is made by dialling the regular directory numberof the called subscriber. In order to explain the operations which takeplace in this type of call it Will be assumed that the subscriber atstation 43.12, Fig. 1, desires to call the subscriber at station 4317 onthe same line.

In order to establish the above connection, the subscriber at station4312 will remove his receiver and dial the number of the called station.The removal of the receiver takes an idle link into use and the finderthereof connects with'the calling line. The subscriber then dials thefour digits of the called number and the connector of the link isoperated the same as has been previously described. Assuming that thelink which is used is the one shown in the drawings, relay 304 of theconnector, Figs. 2 and 3, will be operated so as to select the set ofwipers comprising 336, 338, and 339, which are then positioned on thefirst set of contacts in the third level of their associated banks. Thisset of bank contacts is the set to which normal conductors I05, I03 andI04, extending back to the line circuit, Fig. l, are connected. It willbe noted also that the minor Switch is operated responsive to the lastdigit to position its various wipers on the seventh contacts in theirrespective banks. Aside from these differences, theoperation of theconnector is the same as it was before.

Taking up the detailed description atthis point, when relay 302 fallsback at the end of the impulses for the last digit, a circuit iscompleted over which the test relay 209 is connected to the test wiper336, which is now in engagement with the test contact of the calledline. since the called line is also the calling line, there will be aground potential on conductor I05 and the test relay 209 will pull up.Relay 209 remains locked up after relay 305 falls back and at 250connects a busy tone to the calling line. So far, therefore, theoperation corresponds to the normal operation in calling a busy line.

In this case, however, the calling subscriber expects to hear the busysignal, as he knows that he is calling another subscriber on his ownline, so he merely replaces his receiver for a short interval, longenough to signal the called party. When the receiver is hung up at thecalling station, the line relay 204 falls back and breaks the circuit ofthe slow acting relay 206. Line relay 204 also places ground on the testwiper 330 in order to provide a holding circuit for maintaining theconnection after relay 206 falls back, this holding circuit extendingfrom ground by way of 234, 222, 241, 253, (busy relay 200 being nowenergized), wiper 352, contacts of relays 303 and 304, test wiper 336,conductor I05, I00, Fig. 1, H3, H8, wiper I26, I41, and I52 to holdingconductor I12. Ground on the holding conductor I12 will hold up relaysMI and I01, Fig. 1. Also a branch may be traced from conductor I12 byway of 223, 243, and 248 to relay 200, which serves to hold up relay 208after relay 206 has deenergized. When relay 206 falls back, it closes acircuit for relay 202 at 238, said circuit including the contacts 25I ofthe now Upon energizing, re-

energized busy relay 209.

Relay 202 also dislay 202 locks itself at 229. connects ground from linerelay 204 at 225, and opens the trunk conductors I10 and HI at 226 and221. Finally, at 230 relay 202 closes a circuit for relay 2II, whichenergizes and locks itself at 212. Relay 2II upon energizing breaks onecircuit of relay 306 at 261, but relay 306 holds up over another circuitincluding wiper 35I of the minor switch, now setting on its seventhcontact. Relay 2 also closes at 210a circuit for relay I, which locksitself at 3I2 and completes the ringing circuit in the manner formerlydescribed. I i

The bell at the called station now begins to ring intermittently in theusual manner. After a short interval the calling subscriber will againremove his receiver, and the called subscriber will also take off hisreceiver in order to answer the call. A bridge is accordingly placedacross the line which operates the ring cut-off relay 2 I3. Relay 2I3locks itself at 216, breaks the circuit of relay 300 at 280, and breaksthe circuit of relay 30I at 28I. Relays 306 and 30I accordingly fallback. Relay 2I3 also closes the circuit of relay 2I2, which accordinglyenergizes and closes the heavy talking conductors at 214 and 215. Thislatter operation connects up the back bridge relay203, which energizesover the line circuit through the connector wipers, feeding current forthe transmitters at the calling and called stations. Upon energizing,relay 203 closes acircuit for relay 201 at 233. Relay 201 operates whenits circuit is closed and locks itself at 24I. At 240 and 242 relay 201supplies holding ground for various energized relays in the connector,thus providing against the deenergization of relay 200. For a similarreason relay 201 opens the release magnet circuits at 244, and at 286places a shunt around contact 241 of relay 208. This latter is tomaintain ground on the test wiper. The circuit of relay 200 is broken at243 when relay 201 energizes and relay 208 therefore falls back, but theconnection is not released owing to the continued energization of relay20?. The maintaining of the connection therefore depends on thecontinued energization of back bridge relay 203, which controls relay201.

The calling and called subscribers may now converse,'and when they getthrough they will both replace their receivers. This brings about thedeenergization of back-bridge relay 203. Relay 203 falling back breaksthe circuit of relay 201. When relay 201 deenergizes, the link circuitis released in the manner previously explained.

The operations involved in making certain representative trunk callswill now be explained. It will be assumed that the exchange beingdescribed is connected with a distant manual ex- 1' terminated in thefirst five sets of contacts in 1- the third level of the second hundred.These trunks are therefore accessible to the wiper set comprising testwiper 330 and, line wipers 332 and 333. -The first trunk of the group isindicated in the drawings, Fig. 3, and comprises conductors 350, I, and352. Each trunk may have a. line circuit similar to the linecircuit-shown in Fig. 1, and at the manual exchange may ter minate in ajack and drop, or similar well known ring down signalling equipment.From the location of the trunks in the connector banks as explained, theline selecting digits assigned will be 2, 3 andl. Adding the digit 1 tooperate the minor switch, the complete number of the trunk group will be2311.

Assuming that the subscriber at station I3I2 desires to extend a call tothe manual exchange, he removes the receiver, whereupon an idle linkcircuit is taken into use in the manner previously explained. Assumingthat the link shown inthe drawings is the one which handles the call,the finder, Fig. 1, will connect with the calling line and extend it tothe connector, Figs. 2 and 3. The line relay 204 will thereforeenergize, followed by the energization of relays 206, 200, 2I3, and'2I2, all as previously explained.

The calling subscriber will now start to dial, the first signal dialledbeing the digit 2. Line relay 204 therefore falls back twice momentarilyand sendstwo impulses to the vertical magnet 2I4 and to the slow actingrelay 302 in parallel therewith. Responsive to these impulses, thevertical magnet advances the switch shaft two steps, thereby bringingthe vertical wiper 320 into engagement with the second contact in itsbank. The slow acting, relay 302 holds up during the impulses and fallsback after the impulses cease. Upon deenergizing, relay 302 closes acircuit for relay 2II by way of 246, 3I3, 258, 290,

wiper .320-and contact engaged thereby, and

'- followed by the deenergization of relay 2 I2.

upper winding of relay 2| l to'battery. Upon en'- ergizing, relay 2Hlocks itself at 212. In addition, relay 2H closes a circuit for therelease magnet 2I5, this circuit extending from ground by Way of 246,M3, 258, 213, and off normal contact N2, to the release magnet 2|5. Uponenergizing, the release magnet 215 restores the switch shaft in theusual manner. Also the release magnet closes a circuit for operatingrelay 210, which extends from ground by way of 246, 3l3, 258, 299, 21!,upper winding of 2H), and release magnet 2|5 to battery. Relay 2l0operates in the above circuit as soon as the off normal springs 0N2shift back on the restoration of the shaft and locks itself at 26!.Relay 2l0 also breaks the locking circuit of relay 2| I at 260, andbreaks the circuit including its own upper wind ing and the releasemagnet at 258. Accordingly relay 2 and release magnet 2l5 deenergize.

It will be seen that as a result of the dialling of the digit 2 theconnector switch has been operated and released and that the ofi normalrelay 210 has been energized and locked up. It will be appreciated thatthis has been accomplished without energizing either of the wiperselecting relays 303 and 304. The connector therefore now has access toall lines in the second hundred, which are reached by way of thenormally connected set of wipers.

The calling subscriber maynow dial the next digit 3. As a result, theswitch shaft is advanced three steps by means of the vertical magnet 2M.At the end of this operation, relay M3 is deenergized in the mannerpreviously explained, Thus the impulsing circuit istransferred to therotary magnet 303.

The calling subscriber may now dial the next digit 1, as a result ofwhich the rotary magnet 343 is operated to rotate the switch shaft onestep, bringing the wipers 330, 332, and 333 into engagement with thefirst set of contacts in the third level of their respective banks.Relay 302 of course is operated in parallel with the rotary magnet 343and operates relay 305, which in turn brings about the energization ofrelay 306 in the manner previously explained. Relay 300 transfers theimpulsing circuit to the stepping magnet 32'! of the minor switch.

The calling subscriber may now dial the last digit of the number, whichis also the digit 1. From this point on somewhat different operationsare involved, and the explanation will be given more in detail.Responsive to the dialling of the digit 1, relay 204 falls back once andsends one impulse to the stepping magnet 32'! and slow acting relay 302in parallel, the stepping magnet 32! operating to advance the wipers ofthe minor switch one step. Relay 302 operates and closes a circuit forrelay 305, which operates also. After the impulse ceases, relay 302falls back and closes the usual test circuit, which in this case extendsfrom the test wiper 330 by way of normally closed contacts of relays 304and 303, wiper 352 of the 7 minor switch, 3M and 348, to test relay 209.As-

suming now that the first trunk line is busy, conductor 350 will begrounded, test wiper 330 will encounter ground potential, and the busyrelay 209 will energize. Upon energizing, relay 209 closes a circuit forrelay 3!", which will now operate as a stepping relay for the rotarymagnet 343. The circuit of relay 30I extends'from ground by way of 349,341, rotary control bank 26, the first pin in the third level, nowengaged by wiper 326, wiper 320, 3H, 254, contacts controlledby3l2',

28 I, interrupter contact of rotary magnet 343, and winding of relay 30to battery. Upon the closure 'of the above circuit by the busy relay,relay 30! operates and closes a circuit for the rotary magnet 343 at 3.Relay 30! also closes a circuit for slow-acting relay 305 at 3 I 0, thusmaintaining this relay energized in order to maintain the busy relay 209connected to the test wiper. On the closure of its circuit by relay 30l,the rotary magnet 343 operates'and rotates the connector wipers onestep, at the same time opening the circuit'of relay 30L Relay 30Iaccordingly falls back and breaks the circuit of the rotary magnet. Ifthe second trunk of the group is busy also the busy relay 209 willremain energized and the operation will continue, relay 3!]! and therotary magnet 343 operating alternately, the latter rotating the wipersstep by step in search of an idle trunk line.

When an idle trunk line is found, relay 209 will fall back due to theabsence of ground on the test contact'engaged by wiper 330 and thecircuit of relay 30l will be broken. This relay therefore cannot againenergize and the rotation will cease. Slow-acting relay 305 falls back,as it will receive no more impulses from relay 30l, and the usualcircuit is therefore completed for relay 2| I. Relay 2 now pulls up inseries with the cut-off relay of the selected trunk line. The remainingoperations, including the transmission of ringing current over the trunkline, are the same as have been previously explained.

Some additional explanation will now be made in respect of the rotarycontrol bank. This bank and the associated wiper 326 have been neglectedso far because in any connection involving the operation of either relay303 or relay 304 the ground connection to the rotary control bank isbroken and the wiper 326 consequently can have no function. The rotarycontrol bank therefore is in use only when a line in the second hundredis being called, or when the normally connectedset of wipers is beingused. The circuit drawings, Fig. 3, shows only the third level ofthisbank, as this is the level in which the group of trunks to the manualexchange is terminated. There being five trunks in this group,terminated in contacts I to of the third level, as stated, there will befour pins inserted at positions I to 4, inclusive, of the third level ofthe rotary control bank, as indicated in the drawings. Wiper 320therefore can maintain the circuit to the stepping relay 3M throughsuccessive pins as long as busy trunk lines are encountered and the busyrelay 209 is held up. The

fifth pin, corresponding to the last trunk line of the group, isomitted, so that when the wipers are advanced to the fifth set ofcontacts wipers 320 will find no pin to engage and the circuit of relay30| will be broken, whether the fifth trunk line is busy or not. If thefifth trunk line is busy, relay 209 will hold up and will lock itselfwhen relay 305 falls back, and the busy signal will be transmitted tothe calling party in the usual manner.

In addition to the ring down trunks extending to the manual exchange,there may be various other groups of trunk lines, including a group ofdial trunks extending to an automatic exchange. The operations involvedin setting up a connection to an automatic exchange will therefore bedescribed. It will be assumed that there is a group of five one waydialling trunks terminating in the first five contact sets of the ninthlevel of the banks of the second hundred.

That is, these trunks terminate in the ninth level of the banks whichare associated with the normally connected set of wipers comprisingwipers 330, 332, and 333. These trunk lines differ from the ring downtrunks in that they do not have line circuits such as is shown in Fig.l, but the three trunk conductors of each trunk line extend directlyfrom the connector banks to a standard two-wire repeater. There will beaccordingly five repeaters associated with the five trunk lines,respectively, and from the outgoing side of each repeater there will bea two conductor trunk line extending to the automatic exchange. At theautomatic exchange these trunk lines may terminate in line switches orincoming selectors. Since the group of trunk lines terminates in theninth level of the connector banks, and occupies the first five contactsets in that level, the number assigned to the group is the number 91.

Assuming now that the subscriber at station 4312 desires to extend acall to the distant automatic exchange, he will remove his receiver,whereupon an idle link circuit is taken for use. Assuming that the linkcircuit shown in the drawings is the one which is taken for use, thefinder, Fig. 1, will connect with the calling line and extend it to theconnector, Figs. 2 and 3. The connector line relay 204 and other relayswill pull up responsive to the call in the manner previously described.

The calling subscriber will now dial the first digit of the number,which is the digit 9. The line relay 204 accordingly falls backmomentarily nine times and sends nine impulses to the vertical magnet214 and the slow acting relay 302 in parallel. The vertical magnet 214steps the connector shaft nine steps, advancing the various sets ofwipers carried by the shaft until they stand opposite the ninth levelsof their respective banks. The vertical wiper 329 is positioned inengagement with the ninth contact in the vertical bank 328. Also theshaft springs 354 and 355 are operated, the comb 41, Fig. 7, beingarranged to close these springs on the ninth level. The slow actingrelay 302 responds to the first series of impulses in parallel with thevertical magnet 214 and holds up throughout the series of impulses,falling back after the impulses cease. On deenergizing, relay 302 closesa circuit for the off normal relay 210 which may be traced from groundby way of 246, 313, 258, 299, vertical wiper 329 and the ninth contactengaged thereby, and

thence through the lower winding of relay 210 to battery. Uponenergizing, relay 210 locks itself at 261. In addition relay 210performs its usual functions. It also unlocks relay 213 at 259. Relay213 accordingly falls back and permits relay 212 to deenergize. Relay212 transfers the impulsing circuit from the vertical magnet 214 to therotary magnet 343.

The calling subscriber may now dial the second digit of the number,which is the digit 1. Accordingly the line relay 204 falls back oncemomentarily and transmits an impulse to the rotary magnet 343 inparallel with the slow-acting relay 302. The rotary magnet 343 respondsby rotating the switch shaft one step, bringing the wipers 330, 332, and333 into engagement with the first trunk line of the group. Relay 302operates in parallel with the rotary magnet 343, and now since relay 2 I2 has fallen back a circuit is completed for slow acting relay 305,which operates also. Upon energizing, relay 305 closes at 319 a circuitfor the lower winding of switching relay 201, the circuit extending fromground by way of 349, 341, 355, 319, and the lower winding of relay 201to battery. The lower winding of relay 201 is an inefficient winding andconsequently the relay operates only far enough to close its contactmarked X. The closure of contact X completes a circuit for the upperwinding of relay 201 which extends from ground by way of 2152, 256,contact X, and the upper and lower windings of relay 201 in series tobattery. It will be seen that the upper winding of relay 201 is shortcircuited over the previously traced circuit for the lower winding andconsequently the relay remains only partly energized for the time being.

Shortly after the cessation of the impulse to the rotary magnet 343, theslow acting relay 302 will fall back, and thereby a circuit is closedfor connecting the busy relay 209 to the test wiper 330. This circuitmay be traced from test wiper 330 by way of normally closed contacts ofrelays 304 and 303 to the minor switch bank associated with wiper 352.From this point the circuit is completed by way of 356, 346, 354, 314,and 318 to the busy relay 209. If the first trunk line of the group isbusy, relay 209 will energize because of the ground on the contactengaged by wiper 330, closing a circuit for relay 301. In explanation ofthis circuit it should be stated that the ninth level of the rotarycontrol bank 26 is arranged as regards the first five positions inexactly the same way that the third level, shown in the drawings, Fig.3, is arranged. That is, pins are inserted at positions 1 to 4,inclusive, of the ninth level. Accordingly, wiper 326 will now be inengagement with the first pin of this group and the circuit for relay301 will extend from ground by way of 349, 341, rotary control bank 29,first pin of the ninth level, wiper 326, 311, 254, contacts controlledby 312, 291, and interrupter contacts of the rotary magnet 343 to relay301.

Relay 301 operates as formerly described, closing a circuit for therotary magnet at 3| I, and also closing a circuit for the slow actingrelay 305 at 310. The switch wipers are accordingly rotated step by stepuntil an idle trunk line is found, whereupon busy relay 209 will fallback, breaking the circuit of relay 301 at 254, and the rotation of theswitch will cease. Relay 305 now falls back also, since it no longerreceives impulses from relay 30I. Upon deenergizing, relay 305 breaksthe circuit of the lower winding of relay 201 at 319, thus removing theshort circuit from the upper winding of relay 201. During the rotaryoperation, the ground connection to the upper Winding of relay 201through contact X was temporarily disconnected by energization of relay209, but this connection has now been re-established by the falling backof relay 209, and accordingly relay 201 now energizes fully over thecircuit which extends from ground by way of 262, 256, contact X, andboth windings of the relay in series to battery. Upon energizing relay201 looks itself to the holding conductor 112. Relay 201 also opens therelease magnet circuit at 291, opens the impulsing circuit at 222, andat 223 it disconnects the holding conductor 1'12 from the slow actingrelay 208 and connects it instead to the test wiper 330. In addition,relay 201 connects the trunk conductors 1'10 and 111 direct to thewipers 332 and 333, respectively, at contacts 220 and 221, at the sametime disconnecting these trunk conductors from the line relay 204. Relay204 a cordingly falls back and breaks the circuit of relay .206.

The two trunk conductors I10 and Ill and the holding conductor "2 nowextend via the connector wipersto three conductors of the selectedtrunk. It follows that before the relay 206 of the connector can fallback, the line and release relays'of the repeater associated with theselected trunk will energize, and the latter relay will place ground onthe holding conductor to maintain the connection.

The calling subscriber will now dial the necessary remaining digits tocomplete the connection in the automatic exchange and these digits arerepeated by the repeater in the well known mariner. Release of theconnection is accomplished by hanging up the receiver at the callingstation, which drops the line and release relays of the repeater. Therelease relay falling' back removes ground from the holding circuitincluding conductor I12 and the link circuit is restored as previouslydescribed.

From the preceding explanationit will be clear that another group ofring down trunks could be terminated in the sixth, 7th, 8th, orlOthlevel and could be reached by dialling a three digit number. Such agroup of trunks might be a group of toll trunks leading to the tollboard in an adjacent exchange. Assuming these trunks are terminated inthe 10th level (of the second hundred), the number assigned would be011. In calling the toll operator over one of these trunks, the firstdigit 0 will operate the connector shaft to the 10th level and at thesame time will operate relay 2H1 by means of wiper 329. The second digit1 will rotate the connector shaft one step, whereby wipers 33B, 332, and333 are set on the first trunk line of the group. The third digit 1 willoperate the minor switch, whereupon automatic trunk hunting will takeplace and an idle'trunk will be selected. The hunting movement iscontrolled through the rotary control bank, which has pins inserted atthe 10th level, as explained in the case of the 3rd and 9th levels.

The invention having been described, that which is considered tobe newand for which the protection of Letters Patent is desired will bepointed out in the appended claims.

What is claimed is:

1. In an automatic exchange switchboard, a frame comprising four uprightmembers secured in spaced relation to each other, thereby forming acentral mounting space for switches and a mounting space for banks oneach side thereof, a series of base plates secured one above the otherin said central space, each plate having mounted thereon a finder and aconnector, means for mounting finder banks in the space on one side ofsaid central space, and means for mounting connector banks on the otherside.

2. In an automatic exchange switchboard, a frame comprising four spacedupright members, a link comprising a finder switch and a connectorswitch, a base secured to the two inner upright members and supportingsaid finder at one end and said connector at the other, and bankssupported between the respective switches and adjacent outer uprightmembers of the frame.

3. In an automatic exchange switchboard, a plurality of links eachcomprising a finder switch and a connector switch, a base for each linkon which the two switches thereof are mounted together to form a unitand a frame on which said units are mounted one above the other inhorizontal position.

4:. In an automatic exchange switchboard, a link comprising a finderswitch and a connector switch, each having a wiper shaft, a base plate,means securing the finder switch to said base plate at one end thereofwith the shaft extending beyond the end of the base plate, means forsimilarly securing the connector switch to the said base plate at theother end, and relays for controlling said switches mounted on said baseplate between the switches.

5. In an article of manufacture, a switching unit comprising a baseplate, a finder switch mounted on one end of said plate, a connectorswitch mounted on the other end, said finder and connector each having awiper shaft, relays mounted on said plate between the switches forcontrolling the same, and means including certain of said relays fordirectly connecting the wipers of the finder with the wipers of theconnector.

6. A large capacity switch and mounting therefor comprising a base onwhich the frame of the switch is secured, a frame including two uprightmembers to which said base is secured, said frame including a thirdupright member, bank rods extending between said third upright and theswitch frame, banks supported on said rods, and a bearing for the switchshaft also supported on said rods.

7. A large capacity switch comprising a plurality of sets of banks andwipers, also a vertical bank for controlling wiper selection, a metallicstrip secured to two of said banks, means for mounting said verticalbank on said strip, terminal blocks also mounted on said strip, andwires connecting the wipers of the switch with said terminal blocks.

HARRY P. MAHONEY.

